Question

A pendulum consists of a 3.1 kg stone swinging on a 3.8 m string
ofnegligible mass. The stone has a speed of 7.9 m/s when it
passesits lowest point. (a) What is the speed when
thestring is at 57° to the vertical? (b) What
isthe greatest angle with the vertical that the string will
reachduring the stone's motion? (c) If the
potentialenergy of the pendulum-Earth system is taken to be zero at
thestone's lowest point, what is the total mechanical energy of
thesystem?